The 8/2 crash-hunt bisection attempt with ?collab=0 was silently invalid: the
flag only gated the attach, while the boot fan-out joined the doc room and
materialized the target file from the ydoc regardless (the "collab=0" prod
log shows both, plus an attach). The flag now also skips the doc-room join —
the file falls back to the plain fetch path — making it a real lever for the
warm-siblings crash bisection (ydoc-vs-sexpr file source, the next suspect
after sibling restage and collab attach were exonerated) and an honest
user-facing escape hatch.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_019SE4o46Lnq3hF574FFq8x4
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